This invention is concerned with providing an improved, more economical method for the production of L-ascorbate 2-sulfate compounds and their associated salts; more particularly, it is directed to such a method which produces these compounds by using L-ascorbic acid or its salts as the starting material, rather than a more expensive derivative of this acid.
In our co-pending patent application entitled "PREPARATION AND USE OF L-ASCORBATE 2-SULFATE COMPOUNDS", Ser. No. 325,650, filed Jan. 22, 1973 and now abandoned, a method was disclosed for the production of L-ascorbate 2-sulfate compounds wherein selected 5,6-acetal derivatives of L-ascorbic acid and their salts were employed as the starting material. The sulfation of these compounds was effected by reacting the acetal derivatives with a base sulfur-trioxide complex in a compatible solvent while maintaining the acid concentration of the reaction medium at a sufficiently low level to prevent inhibition of the desired reaction. This method using apolar solvents produced the desired L-ascorbate 2-sulfate compounds and their associated salts in yields of about 75%, and quantitative yields were obtained by using protic solvents. In either solvent system, the final compounds were essentially 100% pure. These results were shown to be superior to any of the methods previously reported in the prior art.
Although that method proved to be extremely efficient in practice, alternate processes have been sought for several reasons. Most importantly, that method as disclosed requires that certain defined 5,6-acetal derivatives of L-ascorbic acid or the salts thereof, be employed as the starting material of the sulfation reaction. As can be appreciated, in some situations it is desirable to employ simple L-ascorbic acid or its salts without any acetal groups in order to produce the desired compounds. This can occur when the formation or removal of the blocking group serves to increase the cost or complexity of the process.
Therefore, there is a need in the art for a method which produces L-ascorbate 2-sulfate compounds and salts thereof by utilizing L-ascorbic acid or its salts as the starting material of the sulfation reaction. This could serve to lower the costs of producing the valuable end products, as well as simplifying the overall chemistry of the reaction sequence. The latter factor is important when it is desired to use the products of the reaction as additives in food products, because a lesser number of reaction steps generally facilitates purification of the end product.
As further disclosed in our co-pending patent application, certain defined L-ascorbate 2-sulfate salts have been found to be extremely stable sources of vitamin C in food systems. Hence, such salts find utility in the chemical and food processing industries as vitamin additives. Typical examples of these uses involve adding the salts to fruit and vegetable juices, jams, jellies, preserves, pastries, bread and dairy products.
It is, therefore, a primary object of the present invention to provide a method for producing L-ascorbate compounds and their associated salts wherein L-ascorbic acid or its salts are employed as the starting material.
It is another important object to provide such method wherein a lesser number of steps are required in the reaction sequence in order to produce the desired compounds.